# itercusum
> Create an [iterator][mdn-iterator-protocol] which iteratively computes a cumulative sum.
The cumulative sum is defined as
## Usage
```javascript
var itercusum = require( '@stdlib/stats/iter/cusum' );
```
#### itercusum( iterator )
Returns an [iterator][mdn-iterator-protocol] which iteratively computes a cumulative sum.
```javascript
var array2iterator = require( '@stdlib/array/to-iterator' );
var arr = array2iterator( [ 2.0, 1.0, 3.0, -7.0, -5.0 ] );
var it = itercusum( arr );
var s = it.next().value;
// returns 2.0
s = it.next().value;
// returns 3.0
s = it.next().value;
// returns 6.0
s = it.next().value;
// returns -1.0
s = it.next().value;
// returns -6.0
```
## Notes
- If an iterated value is non-numeric (including `NaN`), the function returns `NaN` for **all** future iterations. If non-numeric iterated values are possible, you are advised to provide an [`iterator`][mdn-iterator-protocol] which type checks and handles non-numeric values accordingly.
## Examples
```javascript
var runif = require( '@stdlib/random/iter/uniform' );
var itercusum = require( '@stdlib/stats/iter/cusum' );
// Create an iterator for generating uniformly distributed pseudorandom numbers:
var rand = runif( -10.0, 10.0, {
'seed': 1234,
'iter': 100
});
// Create an iterator for iteratively computing a cumulative sum:
var it = itercusum( rand );
// Perform manual iteration...
var v;
while ( true ) {
v = it.next();
if ( typeof v.value === 'number' ) {
console.log( 'sum: %d', v.value );
}
if ( v.done ) {
break;
}
}
```
[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol
